Ear response compensated volume control apparatus



July 21, 1953 J. M. HANERT 2,646,468

EAR RESPONSE COMPENSATED VOLUME CONTROL APPARATUS Filed Feb. 1, 1950 2 SheetsSheet l OUTPUT SYSTE M -inMr July 21, 1953 EAR RESPONSE C Filed Feb. 1, 1950 J. M. HANERT 2,646,468

OMPENSATED VOLUME CONTROL APPARATUS 2 Sheets-Sheet 2 Patented July 21, 1953 EAR. RESPONSE COMPENSATED VOLUME CONTROL APPARATUS John M. Hanert, Park Ridge, 111., assignor to Hammond. Instrument. Company, Ghicago,,lll.,, a corporation of Delaware Application February 1, 1950', Serial ltd-141,692

7 Claims;

This invention relates generally to apparatus for smoothly varying thetonal output of" an electrical musical instrument with adequate compensation for variations in the response:- of the human ear to tones of different frequencies I and different intensities.

This application is a continuation in part of myapplication for patent Serial No. 592,099 en.- titl'ed. Volume: Control Apparatus: filed in the United States-Patent-Ofilce on May- 5, 1 945.

This application has been abandoned.

A volume or expression control for an electrical musical instrument should meet a number of requirements; It should be capable of smoothly and continuously changing the tonal:

, quencies; a wide range of, lower. bass and higher output of the instrument over a wide dynamic range. It should be rugged enough to withstand harduse and even abuse-throughout the life of the instrument without requiring replacement or servicing, other than routine maintenance. The control should be completely quiet in operation, both mechanically and electrically; throughout the life of the instrument. The control should compensate for the nonuniform frequency response characteristics of the human ear.

It is well-known that sounds having intensities' less than a certain level, known as the threshold of audibility, are inaudible tothe human ear. Moreover, sounds having intensities greater than a level, known as the threshold" of pain, producea sensation of pain inthe ear' in addition to sound. In an electrical musical instrument all useful variations of sound volume must be confined between the upper limit of the threshold of pain and the lower limit of the threshold of audibility.

It is also well-known that the threshold of audibility is at its lowest level for sounds hav ingintermediate frequencies within the normal range of the human voice and that the-level of the threshold increases for sounds of both higher and lower frequencies. Of course, very low frequency sounds such as those below about 16 C. P. S., and sounds of very high frequencies, such as those above about 20,000 C. P. S; are inaudible to most people. Furthermore, the level of the threshold of pain is somewhat higher for voice range frequencies than it is for relatively higher treble and lower bass frequencies.

The tones which may be produced by an electrical musical instrument, such as an electric organ, may extend over a very wide frequency range, from about 30 C. P. S. to about 10,000

C. P. S. for example. Such rangeincludes, in ad'-' treble frequencies. As generated, tone signals of all. frequencies:- usually have approximately equallamplitudes. For; moderately great volume levels it is musically satisfactory to sound tones of all frequencies at. approximately equal intensities, and. thus the volume control apparatus and the output. system of. the. organ may have a flat frequency response. for. such volume levels. It desirable, by means of the volume control, to reduce the tonal output. of the instrument to. the threshold of audibility without seriously disturbing; the apparent balance. among tones of various frequencies. Because of the relative in sensitivity of the human ear to very low and very high. frequency tones, the response of the volume control together with the output. system should be considerably greater for such low and high frequenciesthan. forintermediate or voice frequencies when the control is adjusted to provide a. barely audible tonal. output. It is especially important-that even at very low volumelevels the low frequency or bass tones be maintained, at an audible: level, because the: bass tones, to an important extent, determine the over-all musical character: of: the tonal. output of the. instrument.

Since the: human car: will toleratev greater intensities; of. intermediate or voice frequencies than of. very lowand very high frequencies, the highest possible useful volume may be obtained only if the volume.- control apparatus together with. the outputsystem attenuates very low bass and very high treble-frequencies somewhat,v so that. the intensities of such frequencies do not exceed the threshold of pain. when the control is adjusted for maximum volume. the high treble. and low bass responses of the volume control together with the output system should be somewhat smaller than the intermediateor voice frequency response when the volume control is adjusted for maximum volume.

Consequently an adequate volume control for an electrical musical instrument must have frequency response characteristics which change radically as the. volume adjustment is. changed.

The bass response, and to a lesser extent thetreble response, relative to the intermediate frequency responseyshould beboosted as; the volume is reduced. Such: volume control compensation is variously known as ear response. compensation,

. bass: compensation orv bass. boosting;

/ None of the known volume. controls for electrica'l musical instruments satisfy all the above requirements. The. principal object of this invention. is to provide.- volume. control. apparatus.

Therefore,

for an electrical musical instrument which satisfies these requirements.

Specifically, an object of this invention is to provide volume control apparatus which will pro duce smooth, continuous and step-free variation of the tonal output of an electrical musical instrument rather than volume variation in finite steps which has characterized many prior art volume controls.

A further object is to provide a volume control which will withstand long and hard service without requiring attention.

A further object is to provide a volume control which will operate quietly without producing electrical transients throughout the life of the instrument.

A further object is to provide volume control apparatus which has frequency response characteristics which change as the volume is varied in order to compensate for the nonuniform frequency and intensity response characteristics of the ear.

' A further object of this invention is to provide such volume control apparatus which may readily be manufactured at low cost.

Other objects and advantages together with an understanding of the basic principles of this invention may be derived from the following description together with the drawings in which:

Figure 1 is a wiring diagram of an illustrative embodiment of this invention.

- Figure 2 is an elevational sectional view, taken on the plane 22 of Fig. 3, of a variable capacitor forming a part of the illustrative embodiment.

Figure 3 is an elevational sectional view of the capacitor taken on the plane 33 of Fig. 2.

Figure 4 illustrates suitable apparatus for operation of the variable capacitor by means of an organ expression pedal. Referring to Fig. 1, volume control apparatus is illustrated which is adapted to provide musical tone signals of variable amplitude from its output terminals i8 and I2 for transmission to the output system It of an electrical musical instrument in response to constant amplitude tone signals impressed upon input terminals I8 and 2B of the control apparatus by the musical tone signal generating system 22 of the instrument. The input terminal is grounded while the input terminal I8 is connected with the control grid of a coupling pentode 24 by means of a radio frequency filtering resistor R28. The input terminals i8 and 2-2 are shunted by a grid resistor R28. The plate of the pentode 24 is connected withan anode voltage supply terminal +285 v. by means of a parallel mesh comprising a load resistor R3!) and a small high frequency by-pass capacitor C32. An adjustable amount of negative feedback is provided by a small adjustable capacitor C34 connected between the plate of the pentode 2-1 and the input terminal 18. Further degenerative action is provided by an unbypassed cathode resistor R36 connected between the cathode of the pentode 24 and ground. The screen grid of the pentode 24 is connected with the +285 v. terminal by a resistor R38 and is by-passed to the cathode by a capacitor C40.

The pentode 24 serves as an amplifier and coupling tube and provides amplified tone signals corresponding with those supplied by the generating system 22. The anode of the pentode 24 is connected by a conductor 42 with a set of stationary plates 64 of a variable capacitor C46. A second set of stationary plates 48 is connected with the anode of the pentode 24 by means of an ear response compensated attenuating mesh 55. The attenuator 50 may comprise a resistor R52 shunted by a capacitor C54 connected between the anode of the pentode 24 and a terminal 5'6, a capacitor C58 in series with a resistor REG connected between the terminal 56 and ground, a resistor R62 in parallel with a capacitor C64 connected between the terminal and the set of capacitor plates 48, a resistor RG6 shunted from the set of capacitor plates 48 to ground and a capacitor C63 in series with a resistor R70 likewise shunted from the plates 48 to ground.

The mesh 50 attenuates high and low frequencies less than a middle range of frequencies. For middle range frequencies the mesh 50 provides two cascaded frequency selective voltage divider sections individually including a series arm and a shunt arm. The first series arm comprises R52 in parallel with C54 and the first shunt arm comprises C58 in series with R58. A signal voltage from the pentode 24 divides between the first series arm and the first shunt arm, and only the portion which develops across the shunt arm is transmitted to the second voltage divider. The series arm of the second voltage divider section comprises B62 in parallel with C84 and the second shunt arm comprises Riit in parallel with the series combination of C68 and R10. The signal voltage received from the first voltage divider section divides between the second series arm and the second shunt arm, and only the portion of the Voltage across the second shunt arm is transmitted to the stationary plates 48 of C45.

For low bass frequencies the capacitive reactance of C58 is much larger than the resistance of R52 because the capacitive reactance of C58 increases as the frequency decreases. Therefore the attenuation of the first voltage divider section is very small for such low bass frequencies. Moreover the capacitive reactance of Cfifi is much greater than the resistance of R62 for low bass frequencies, and so the second voltage divider section attenuates low frequency signals much less than middle frequency signals. However, the shunting effect of R together with the series impedances of R52 and R52 provides some attenuation at low frequencies.

The capacitive reactance of C54 decreases as the frequency increases and becomes much less than the individual resistances of R52 and R53 to high treble frequency signals. Therefore the first voltage divider section attenuates high frequency signals relatively very little. Likewise the capacitive reactance of C64 for high frequency signals is much less than the individual resistances of R52, R10 and R66, and attenuation of high frequency signals by the second voltage divider section consequently is relatively small.

For the reasons explained above the mesh 59 attenuates low bass frequencies signals and high treble frequencies signals relatively much less than middle frequency range signals. C54 and C64 permit high frequency signals to pass to the capacitor plates 4-8 of the C46 with little attenuation. For low bass frequencies the impedances of the shunt arms of the mesh 55 are relatively very high because of the high reactances of C53 and C53, and low bass frequency signals consequently pass to the plates 48 through R52 and R62 with little attenuation.

The variable capacitor C46 includes a set of scanner plates I4 which, is movable into capacitive pickup relation with either of the sets 44 and .48 of stationary plates or partially in any selected ratio into capacitative relation with said sets of plates. The scanner plates I4 are connected with the grid of a phase inverter triode 16 which may be one unit of a double triode tube as illustrated. A capacitor C82 shunted by a grid return resistor R84 connects the scanner plates I4 with a terminal I8 which is by-passed to ground by a large bias filter capacitor C80. The terminal I8 is connected directly to the grid of a second phase inverter triode B6 and is connected by a resistor R38 with a positively charged grid bias source terminal v. The cathodes of the triodes l6 and 86 are connected to ground by a high resistance common cathode biasing resistor R90. The anodes of the triodes I6 and 80 are connected with an anode supply terminal +290 v. by individual anode load resistors R92 and R94 respectively, and with the output terminals I0 and I2 by individual coupling capacitors C96 and C98 respectively. The output terminals I0, I2 are connected with the output system It which may include, for example, a power amplifier and a speaker (not shown).

According to their position, the scanner plates I4 pick up signals from either the stationary plates 44 or 48 or from both sets of plates 44 and 48 jointly in any selected proportion, and the signals are impressed upon the grid of the triode l6. Resistor R84 provides a direct current path from the grid of the triode 16 to ground through R88 and the grid bias source and also may slightly modify the low frequency response of the volume control apparatus together with the amplifiers and the output system It. C82

may have a capacitance such that its capacitive reactance at the lowest frequency which is to be transmitted, by the apparatus is of the same order as the resistance of R84, and so for intermediate and high frequencies the capacitive reactance of C82 is much less than the resistance of R84. Thus for intermediate and high frequencies the shunting effect of R84 is negligible and the capactive voltage divider comprising C46 and 082 has a uniform frequency response for such intermediate and high frequencies. At the lowest frequencies to be transmitted, however, the shunting effect of R84 may produce some attenuation. The capacitance of C80 is great so that even at the lowest frequency to be transmitted its capacitive reactance is negligible relative to the resistances of R84 and R88, and so the terminal i8 is maintained nearly at ground potential for signal voltages. out any ripple components present in the +20 v. bias supply voltage.

The triodes I6 and 86 provide phase inversion and amplification. Signals develop across the high resistance common cathode resistor R90 which have amplitudes about one-half the amplitudes of the signals impressed upon the grid of the triode l6 by the scanner plates I4. Since the grids of both triodes l6 and 86 are returned to the terminal I8 which is at ground potential for signal voltages, the signals across R90 appear in the grid-cathode circuits of both triodes i6 and 86, providing negative feedback for the triode I6 and reversely phased input signals for the triode 86. The grids of the triodes I6 and 86 are returned to thepositive grid bias source terminal +20 v. in order to counteract part of the excessively great negative grid bias provided by the voltage drop across R90 and thus to provide a suitably small negative. grid-cathode bias for the C80 is provided primarily to filter triodes I6 and 86. Output voltages which are approximately balancedwith respect to ground are provided by R92 and R94 and are coupled to the output system It through C06 and C93.

The mechanical details of the variable capacitor C46 are illustrated in Figs. 2 and 3. The scanner plates I4 are mounted on a bracket I00 secured to an insulating plate Hi2 which is mounted on a rotatable shaft I04 by means of a U-shaped arm I06 secured to a hub I08. A set screw H0 which engages the shaft 584 permits longitudinal adjustment of the hub I03 along the shaft I04 over a limited range. A control arm H2 is secured to the end of shaft I04 by means of a bushing II4. Suitable bearings III and {I3 mounted on a housing H5 support the shaft Hi4. Longitudinal movement of the shaft is prevented by a set screw collar IIl.

Thestationary plates 44 and 48 are secured by brackets H8 and I20 respectively to an insulating base plate I22 secured to the housing I55.

The adjustable capacitor C34 is mounted on a partition I24 within the housing H5. An electrical connection is made to the scanner plate 74 by means of a flexible wire (not shown) connected with a soldering lug I26. Connections with the stationary plates 44 and d8 are made to soldering lugs I23 and IEG respectively. The, housing H5 is normally groundedlto provide shielding for the variable capacitor C46 and the adjustable capacitor 034.

The full line position of the scanner plates I4 and the control arm H2 is the minimum volume setting with the scanner plates I4 meshed with the stationary plates 48, while the dotted line position of the scanner plates I4 and the control arm H2 is the maximum volume setting with the plates I4 meshed with the stationary plates 44. The scanner plates 14, together with the control arm H2, are continuously movable between these extreme positions so as to mesh partially with both sets of stationary plates 44 and 48 in any desired proportion.

In Fig. 4 the variable capacitor C-it is mounted within a console I34 of an electrical musical instrument having an expression pedal I36 pivotally mounted at the front of the console I34. A linkage rod I38 pivotally connected with the control arm I I2 and with a bracket E40 mounted on the pedal I36 provides an operating connection between the pedal I35 and the control arm M2. The pedal I36 may be tilted between limits defined by a front stop E42 and a rear stop I44. Whenthe pedal 93E is'in its full line position against the front stop 42 the linkage rod I38 moves the control arm IIZ so that the variable capacitor C45 is in its minimum volume position, and when the pedal 35 is in its dotted line position against the rear stop E44 the control arm H2 is moved to its maximum volume position by the linkage rod I38.

When full volume is desired the musician tilts the expression pedal I36 to its dotted line position against the rear stop E44, thus moving the scanner plates I4 into the dotted line position (Fig. 3) in capacitative pickup relation with the stationary plates 44. Referring to Fig. 1, tone signals will then be transmitted through the cou pling pentode 24 and the conductor 42 to the stationary plates 44 and thence by capacity coupling to the scanner plates I4, the grid of the triode l6 and finally to the output system I6. The components of the apparatus in Fig. 1, including the generating system '22 and the output system I61, are so proportioned that a direct connection by the conductor 42 from the plate of the pentode 24 to the stationary plates 44 provides frequency response characteristics suitable for a hi h volume level. Very low frequencies may be attenuated somewhat by the shunting effect of R84 while very high frequencies may be attenuated by the shunting effect of C32, and the response for intermediate frequency signals may be somewhat greater than for high and low frequency signals. In some cases it may be desirable to modify the frequency response characteristics at high volumes by providing a suitable filter, which may be in series with the conductor :2.

When a musician desires a minimum volume level he tilts the expression pedal I36 to its full line position against the front stop i 32 so that the scanner plates 14 are moved into capacitative pickup relation with the stationary plates 48. Tone signals then are transmitted through the attenuating mesh 5% to the stationary plates 48 and thence capacitively coupled to the scanner plates i i. The attenuator 50 has signal transmission frequency characteristics suitable for maintaining a proper balance among tones of different frequencies at a low volume level. For example, the attenuating mesh 50 may attenuate signals of intermediate or voice frequencies by about 30 decibels (db), while attenuating very low frequencies only about 6 db and very high frequencies only about 10 db. Such an attenuator 50 together with the other components of Fig. l compensates approximately for the nonuniform frequency response characteristics of the human ear by boosting the high treble and low bass responses of the volume control apparatus to relatively higher levels than the intermediate frequency response at low volume levels. Consequently, bass tones and high treble tones are maintained at audible levels even when the overall volume of the tontal output of the instrument is at a minimum.

When intermediate volume levels are desired the expression pedal B8 is tilted to some suitable position between its full and dotted line positions in Fig. 4, thus moving the scanner plates i l into capacitative pickup relation with both sets of stationary plates a l and 48 jointly in any selected proportion. One such position of the scanner plates is illustrated in Fig. 1. Tone signals then are capacitively coupled to the scanner plate it from both sets of stationary plates it and 48, and the volume control has intermediate frequency response characteristics. If the scanner plates Hi are moved smoothly from their dotted line position in Fig. 3 to their full line position the signal transmission characteristics chan e smoothly as the volume decreases smoothfrom maximum to minimum.

Since there are no sliding or rolling contacts in the volume control apparatus, complete freedom from noisy operation is assured for the life of the instrument. The volume control apparatus is simple, trouble-free, rugged and inexpensive. It will be apparent to those skilled in the art that volume control apparatus according to this invention meets all the requirements for service as an expression control in an electrical musical instrument.

In order to facilitate the practice of this invention, illustrative values of the components employed in the embodiment illustrated in Fig. 1 are tabulated below. These illustrative component values are given in order that the disclosure of this invention may be complete and specific.

The specific illustrative values set forth should not be construed to limit the scope of this invention because those skilled in the art will understand that the values of the components may be varied over a considerable range without departing from the basic principles of this invention. A complete statement of the true scope of this invention will be found in the appended claims.

The capacitance between the plates 64 and 14, as well as between plates 48 and I l, when the plate i4 is in registry with either of these plates,

' may be exceedingly low, in the order of micromicrofarads. Thus the scanner plate i4 is effective solely as a means for smoothly varying the overall dynamic response, as well as the over-all frequency response, from a point of high volume when plate 74 is in registry with plate 44, to an extreme of low volume when plate '14 is in registry with plate 48. It is to be noted that when 74 is partially in registry with both 44 and 68 an intermediate over-all intensity and frequency res onse curve results.

In the following table the values of resistors are given in ohms, thousands of ohms (K), or megohms (meg). Values of capacitors are given in microfarads.

R23 .33 meg. R28 5.6 meg. R30 .27 meg. C312 .0002 C34 .000015 R35 1500 ohms 1.5 meg. C53 .25

R52 1.8 meg. C5 3 .0002 C58 -l .002 R30 68K R52 1.8 meg. C6 .0002 R36 5.6 meg. C68 .001 R70 68K C .25

C82 .0005 R8 1 5.6 meg. R88 .18 meg. R90 39K R92 .47 meg U94 .47 meg C .05

A specific illustrative embodiment of this in vention has been described in order that those skilled in the art may readily understand the fundamental principles of this invention. However, those skilled in the art will be able to apply the principles disclosed herein to provide structures which may differ in their details from the specific embodiment described herein. Therefore the scope of this invention should not be limited by the deteails of the above disclosure except a set forth in the appended claims which are intended to include such modifications and equivalents which are within the true scope of this invention.

I claim:

1. In an electrical musical instrument including a tone signal generating system having an output and an output system having an input; volume control apparatus, including first and second adjacent capacitor plates, a scanner plate relatively movable to be in capacitative pickup garagesrelation-with either of said first orlsecond plates, or partially in any selected ratio in capacitative relation with said plates, means coupling said first plate with the output of said generating system, said means having frequency response characteristics suitable for a maximum volume by attenuating the low bas frequencies to a greater extent than the medium treble frequencies, attenuating means coupling said second capacitor plate with the output of the generating system, said attenuating meanshaving frequency response characteristics suitable for a minimum volume by attenuating intermediate voice frequencies to a much greater extent than the bass and higher treble frequencies, and means coupling said scanner plate with the input of the output system, whereby compensation is made for the nonuniform frequency response characteristics of the ear.

2. An ear response compensating volume control for an electrical musical instrument, comprising an input terminal, first and second adjacent stationary capacitor plates, a scanner plate relatively movable into capacitative pickup relation with either of said plates or partially in any selected ratio into capacitative pickup relation with both of said plates, signal transmission means coupling said first capacitor plate with said input terminal, attenuating means coupling said second capacitor plate with said input terminal, said attenuating means providing substantially greater attenuation of signals in the voice frequency range than of low frequency signals, an output terminal, and means coupling said scanner plate with said output terminal.

3. In an electrical musical instrument, a source of tone signals, first and second capacitor plates, signal transmission means coupling said first plate with said source, an attenuator mesh providing substantially greater attenuation in the intermediate voice frequency range than said signal is attenuated by the transmission means coupling said second plate with said source, a scanner plate relatively movable into capacitative coupling relation with either. ofsaid first and second plates or partially in any selected ratio with both of said first and second plates, substantially capacitive load impedance means connected with said scanner plate, an output system, and a means coupling said scanner plate with said output system.

4. In an electrical musical instrument, a pair of output terminals of a source of a plurality of tone signals including voice frequency range signals as well as lower bass frequency signals and higher treble frequency signals, first and second capacitor plates, signal transmission means connecting said first plate with one terminal of said source, an attenuator mesh having substantially greater attenuation than said signal transmission means coupling said second plate with the same terminal of said source, the difference in signal attenuating characteristics between said signal transmission means and said attenuator mesh being greater for said voice frequency range signals than for said lower bass frequency and higher treble frequency signals, a scanner plate relatively movable into capacitative coupling relation with either of said first and second plates or partially in any selected ratio with both of said first and second plates, an output system including an electron discharge device having a control grid and cathode, means connecting said scanner plate with said control grid, mea-nskccnnecting said cathode to the other terminal ,of the source, and a low value capacitor connected betWeen-the controlgrid and cathode, wherebythe balance among tone signals of various frequencies is changed as the output volume-is changed by moving said scanner plate, to compensate :for the nonuniform frequency response characteristics of the human ear.

' 5. v:In'an electrical emusical instrument, a source of a plurality of tone signals including .voice frequency range signals as well as lower bass frequency signals and higher treble frequency signals, first and second capacitor plates, signal transmission means coupling said first plate with said source, an attenuator mesh having substantially greater attenuation than said signal transmission means coupling said second plate with said source, the difference in the signal attenuating characteristics of said signal transmission means and said attenuator mesh being substantially less for said bass frequency signals than for said voice frequency range signals, a scanner plate relatively movable into capacitative coupling relation with either of said first and second plates or partially in any selected ratio with both of said first and second plates, an output system, and means coupling said scanner plate with said output system, whereby the balance among tone signals of various frequencies is changed as the output volume ischanged by moving said scanner plate to compensate for the nonuniform frequency response characteristics of the human ear.

6. In an electrical musical instrument, a source of a plurality of tone signals including voice frequency range signals as well as lower bass frequency signals and higher treble frequency signals, first and second capacitor plates, signal transmission means coupling said first plate with said source, an attenuator mesh having substantially greater attenuation than said signal transmission means coupling said second plate with said source, the diiference in signal attenuating characteristics between said signal transmission means and said attenuator mesh being less for said treble frequency signals than for said voice frequency range signals, a scanner plate relatively movable into capacitative coupling relation with either of said first and second plates or partially in any selected ratio with both of said first and second plates, an output system, means coupling said scanner plate with said output system, and additional means for attenuating the higher treble frequencies and the lower bass frequencies in the signals transmitted from the source to the output system irrespective of the volume path coupling said source with said output system, an ear response compensated attenuator forming a part of said low volume .path for compensating for the nonuniform response characteristics of the ear by attenuating medium voice frequencies to a greater extent than the higher treble and lower bass frequencies are attenuated, and a variable capacitor forming a part of said high volume path to vary the transmission of signals through said high volume path relative to said low volume path, whereby the balance among tone signals of various frequencies is changed as the output volume is changed by adjusting said capacitor in order to compensate for the nonuniform response characteristics of the human ear.

JOHN M. HANERT.

References Cited in the file of this patent UNITED STATES PATENTS Number 10 Number Name Date Stevenson Jan. 6, 1931 Barstow June 7, 1932 Eckberg Apr. 26, 1938 Lundry Dec. 2, 1941 FOREIGN PATENTS Country Date Great Britain Aug. 28, 1930 

